Collating machines are frequently used in line with other paper handling equipment as a means for assembling a plurality of sheets of document into a stack. The stack is transferred to a folding stage for folding, if necessary, and then to an insertion stage where the stack is inserted in an envelope. Some collating machines have a dual accumulator which uses two accumulator bays from which completed accumulations are discharged back into a single transport path.
FIGS. 1A and 1B illustrate a prior art dual accumulator. As shown, the dual accumulator 10 has an upper bay 20 and a lower bay 30. A paper path 12 is split into two paths by a deflector 14 so that input sheets can be accumulated in two bays alternately. As shown in FIG. 1A, the deflector 14 is positioned such that a sheet of document transported along the paper path 12 is directed to the upper bay along a paper path 100. After the collation is completed, the collation is released from the upper bay end 22 through a guide 24 along a release path 101. As shown in FIG. 1B, the deflector 14 is positioned such that a sheet of document transported along the paper path 12 is directed to the lower bay along the paper path 100′. After the collation is completed, the collation is released from the lower bay end 32 through a guide 34 along a release path 101′. The collations are alternately released from the upper bay end 22 and the lower bay end 32 back to a single paper path through an exit nip 40. The exit nip 40 is formed by an upper roller 50 and a lower roller 60.
FIG. 2A shows the paper path 101 between the upper bay end 22 and the exit nip 40, and FIG. 2B show the paper path 101′ between the lower bay end 32 and the exit nip 40 in the merging region of the accumulator. In the conventional design, accumulations of short sheets present a problem if the length of the sheets is smaller than the path 101 or 101′. Because once the short accumulations are released from the bay ends, they are temporarily not under the position control of any roller nips. Without such positive control, accumulations would skew or come out of alignment. In some instances, the accumulations might even come to a stop between the roller nips. Thus lack of positive control may cause problems by causing a jam, or by causing other problems in the downstream folding or insertion stages.
Thus, it is advantageous and desirable to provide a method and apparatus for keeping each of the released collations, whether it is released from the upper bay or the lower bay, under a positive control when the collation is in the merging region.